J. Exp. Biol. (1967), 46, 3°7-3i5
With 3 text-figures
Printed in Great Britain
307
CHANGES IN BLOOD PRESSURE, HEART RATE
AND BREATHING RATE DURING MODERATE SWIMMING
ACTIVITY IN RAINBOW TROUT
BY E. DON STEVENS AND D. J. RANDALL
Zoology Department, University of British Columbia, Vancouver, B.C., Canada
{Received 4 November 1966)
INTRODUCTION
There is a paucity of data concerning the changes in circulation occurring during
swimming in fish. Data reported in the literature have been obtained from either
restrained, anaesthetized or operated fish (Greene, 1904; Hart, 1945; Johansen, 1962;
Robertson et al. 1966). Such procedures can have marked effects on fish (Fry, 1957).
It is therefore surprising that little attention has been directed towards measuring
parameters of circulation and respiration in unrestrained, unanaesthetized, intact
fish (Randall, Smith & Brett, 1965). Recently, methods have been developed for
measuring blood pressures using indwelling cannulae (Smith & Bell, 1964; Holeton
& Randall, 1967). These techniques, combined with those of Brett (1964) which use
varying water velocities to produce variations in swimming speeds in fish, permit
measurement of various parameters of circulatory and respiratory systems in swimming fish.
The present study was undertaken to examine the effects of swimming on circulation and respiration using free swimming, unanaesthetized rainbow trout.
METHODS
The experiments were carried out on thirty-nine hatchery-raised rainbow trout
(Salmo gairdneri) weighing between 200 and 600 g. The fish were fed three times
weekly with a food containing beef liver, yeast and canned salmon with sulphamerazine added (1 g./io lb. food) to reduce the incidence of furunculosis (Snieszko,
Gutsell & Friddle, 1948).
A fish was anaesthetized by immersion in water containing 1:10,000 tricaine
methanesulphonate (MS-222). The ventral aorta, dorsal aorta and opercular cavity
were cannulated as described by Holeton & Randall (1967) and Smith & Bell (1964).
The opercular cannulation permitted the measurement of the rate of respiration while
the vascular cannulae allowed measurement of blood pressure in the dorsal and ventral
aorta; that is, blood pressure afferent and efferent to the gills. The subintestinal vein
was cannulated with a polyethylene T-cannula (Clay-Adams PE 50) to record venous
blood pressure. In order to estimate venous bloodflowthe subintestinal vein was cannulated towards the tail and the vessel was tied off anteriorly. Flow was determined as the
time taken to fill a o-1 ml. heparinized pipette. All cannulae were 2 ft. long and filled
with heparinized (1 unit/ml.) Courtland saline for fresh-water teleosts (Wolf, 1963).
20
Exp. Biol. 46, 2
308
E. D O N STEVENS AND D. J. RANDALL
When all cannulae were in place the fish was placed in a respirometer similar to that
described by Brett (1964). Briefly, it consists of a Perspex tube through which water is
recirculated. The fish swims against the current at a rate which is dependent on the
rate of water flow through the tube, which in turn is determined by a variable speed
pump. Fresh water was continuously added to the system (10 l./min.) to ensure an
adequate oxygen supply.
The fish was allowed to recover from the operative procedures in the respirometer
for at least 4 hr. The water was gently recirculated during this period, but the water
velocity was so low that the fish could maintain its position in the tube without
swimming.
After recording pre-exercise levels, the water velocity was increased stepwise once
every minute for 5 min., maintained at a maximum level for 5 min. and then decreased stepwise once every minute for 5 min.
Ventral aortic, dorsal aortic and venous pressures were measured continuously
throughout the experiment and for 30 min. after the cessation of swimming. Opercular
pressures, also measured over the same time period, gave a measure of respiration
rate. The heart rate was determined from the pulse rate on both the ventral aortic and
dorsal aortic blood-pressure records. Pressures were recorded using Statham P 23AA
and P 23BB pressure transducers which had been calibrated against a column of water
and displayed on a Beckman type R Dynograph.
The temperature of the dechlorinated fresh water during the experiments was the
same as that in the holding tanks. The temperature was 10-120 C , however, it never
varied more than ±0-5° C. during any one experiment.
RESULTS
In general the fish swam continuously throughout the period of maximum water
velocity. The tail-beat frequency during this period was about 160 beats/min.
Before exercise ventral aortic blood pressure was 40/32 mm. Hg, dorsal blood
pressure was 29/25 mm. Hg and venous pressure was 9 mm. Hg (Fig. 1, Table 1).
During exercise ventral aortic blood pressure, both systolic and diastolic, increased
by about 40%. The dorsal aortic systolic pressure increased by about 16% and the
diastolic pressure by about 21 %. During recovery from exercise both ventral aortic
and dorsal aortic blood pressures decreased gradually to the pre-exercise level within
30 min. (Fig. 1).
There was no pulse pressure in the subintestinal vein, but during exercise there were
irregular rapid increases in blood pressure (Fig. 3). The maximum venous blood
pressure recorded during each period of the experiment is shown in Fig. 1 as the peak
venous pressure. The minimum venous pressure did not change significantly during
the exercise period. To demonstrate that the venous pressure changes recorded were
not produced by bending of the cannula during swimming, dummy cannulae were
placed in the coelom and outside the body wall. The pressure changes observed in the
venous T-cannula did not occur in the dummy cannulae. Pressure changes in the
dummy cannulae were associated with the body movements and were used to estimate
tail-beat frequency.
The pre-exercise heart rate and breathing rate were 24 and 77/min. respectively.
Changes in the rainbow trout whilst swimming
3°9
Dorsal aortic:
o
systolic
diastolic
S
Venous pressure
1 7
V
o <
10
15
20
25
30
Time (min.)
Fig. 1. Changes in blood pressure in the ventral aorta, dorsal aorta, and subintestinal vein
during and after moderate swimming activity. Points are mean values from at least ten fish.
Table 1. Blood pressures, heart rates and respiratory rates during moderate
exercise in rainbow trout. Values given are means ± standard errors
Blood pressure (mm. Hg)
,
Vent
( » ' = 13)
Condition
Pre-exercise
Exercise
Water
16)
A
velocity
(ft./sec.) Systolic Diastolic Systolic Diastolic
023
40 + i-o
031
050
41 ± 1-2
42 ±1-4
44+1-8
47±i-6
5O±i-6
54±i'i
56±i-6
56 + 1-8
58 + 1-8
57 + 2-0
55±i-9
53±2-i
5O±2-I
32 + 0-9
3 2 ± I-I
34+1-3
3 5 ±i ' 5
37±i'4
40 ± i-6
42±i-3
43 ±i-8
43 ±i-9
45 ±i-9
44±i-9
42 ± 2-0
41 ±2-2
39 + 2-1
49 + 2-2
45±2-i
43 ±2-3
38±i-5
35 + O-9
37±2-i
34±i-9
32±i-g
29± i-o
27 + 0-7
0-71
i-oo
170
1-70
I-70
I-70
I-70
i-oo
071
050
031
Post-exercise
o min.
5 min.
io min.
30 min.
60 min.
Dorsal aorta
023
0-23
023
023
0-23
1
Peak
25 ± i-o
9±io
25±I-I
9 ±I I
9±i-4
10+1-3
33±i"2
32 ±1-2
32±I-I
31 ±1-1
26±II
26+1-0
27 ±0-9
29 ±0-9
29 ± 10
29± I-I
29± I-I
3O±i-4
29±i-3
28 + 1-2
27±I-2
26±I-I
3 0 ± i-o
2 9 ± i-o
28±I-O
27 + i - o
26 ± 10
25 ± i-o
24± i-o
23 ±0-9
—
—
33±I-I
34±i-°
Respiratory
Heart
Minimum (» = 29;1 (n = 10)
A
29 ± 1-2
33±I-I
I-I
A
vein (n = 10)
29 ±1-2
3O± 1-2
3O±I-I
31+0-9
33 ±0-9
33±
Rate (no./nun.)
O UU111H
I I + I-S
I2±I-8
16+1-7
16 ±27
i8±5-o
16 + 3 0
13+ i-6
11 ± 1-5
IO± IO
9± I-I
8±I-I
8 ±I I
8±I-2
7±i-3
—
8±I-I
8±I-2
8+i-o
8 + I-I
47 + 2-5
47 ±2-4
48 ±2-4
50 ±2-3
8 + i-o 5°±2-3
9+I'Z 52±2-2
9+1-2 54 ±2-2
9± i-o 53 ±2-2
9 ±07 54±2-2
9 + 0-8 54±2-3
9 + 09 54 ±2-2
9+10
52 ±2-3
9±i-o 51 ±2-4
8+I-I
50+2-5
8 ± I - I 49 ±2-5
8 ± I - I 48 + 2-7
6 + 0-9 47 + 2-8
6 ± i o 46+ 2-8
—
77±i-9
76±i-5
78±i-3
78 ±2-2
87±2-2
94±2i
98 ±1-9
IOO±2-I
IO2±2'7
99 + 2 3
g6±i-5
87 ±2-2
84±2-3
8I±2-I
79±3"O
78 ±2-2
78 ±i-6
78±i-3
310
E. D O N STEVENS AND D. J. RANDALL
During exercise the heart rate increased by about 15% and the respiratory rate by about
30% (Fig. 2). Both rates returned to the pre-exercise levels within 30 min. after the
exercise period.
Injections of atropine (0-5 ml. of io~3 atropine in Courtland saline) into the pericardial cavity had no effect on the heart rate of the resting trout. The changes in heart
rate occurring during swimming were identical both before and after injections of
atropine into the pericardial cavity. The dose level of atropine, however, was sufficient to block the cholinergic fibres innervating the heart, since stopping water flow
over the gills after administration of atropine did not provoke reflex bradycardia
(Randall, 1966).
100
Respiratory rate
S
80
60
40
0^6
1-2
l~Z
0-7
V
5
-Activity
10
0
> <
10
15
Recovery-
20
25
30
Time (min.)
Fig. 2. Changes in heart rate and breathing rate during and after moderate swimming
activity. Points are mean values from at least ten fish.
Blood flow in the subintestinal vein appeared to decrease during and after exercise
(Table 2). The blood appeared to clot much more readily during and after exercise, so
that an increase in viscosity may account for at least a part of the decreasedflowmeasured
from the subintestinal vein.
DISCUSSION
There have been very few measurements of blood pressure in unrestrained teleosts.
(Randall et al. 1965; Holeton & Randall, 1967). Previous workers have tended to use
restrained fish (Greene, 1904; Hart, 1945; Johansen, 1962). In spring salmon Greene
311
Changes in the rainbow trout whilst swimming
Ventral aortic blood pressure (mm. Hg)
60
K 50
''W^'^l'^''™'^!"!^'
UllUUUIIllllUlllllUUUIIIilllil
nPmMPiPwHpIt
30 sec.
S
—
Dorsal aortic blood pressure (mm. Hg)
60
£
*W*M«HHft
, 30 sec. ,
30 sec.
6B
%
Subintestinal venous jlood pressure (mm. Hg)
10
0
Buccal cavity water pressure
10 sec.
0$0$00}tt0
1 10
sec.
f
Tail-beat frequency
I kft^Uilltart Hill
Pre-exercise
WMMWMJMMJ wMUwuummum
I I lk 1
* 1 1 Ir 1 I t t f ' H i n
^
During maximum
activity
Immediately after
exercise
30 min. after
exercise
Fig. 3. Typical pressure records from the ventral aorta, dorsal aorta, subintestinal vein, the
opercular cavity and a dummy cannula attached to the body wall.
Table 2. Blood flow from caudal musculature measured in subintestinal vein
S.E.
(ml. /min.)
X
Pre-exercise
During exercise
Post-exercise
o min.
io min.
6o min.
O-U4
0094
±
±
00453
00336
0084
0-036
0086
±
0-0318
+
+
00216
00509
(1904) reported a ventral aortic blood pressure of 77 mm. Hg. He also observed
periodic fluxes in blood pressure due to the heart missing every 4th or 5th beat. This
has been observed in the eel (Mott, 1951) and in elasmobranchs (Lyon, 1926). It was
only observed in the present study after exercise. Johansen (1962) reported a blood
pressure of 30 mm. Hg in the bulbus arteriosus of the cod. The fish in his study were
restrained and ventral side up, but not anaesthetized. Robertson et al. (1966) measured
pressures in the ventral aorta of the spring salmon of 82/50 mm. Hg and dorsal aortic
pressures of 44/37 mm. Hg. They stopped the waterflowover the gills when recording
312
E. D O N STEVENS AND D. J. RANDALL
blood pressure, and this initiated a bradycardia reflex as indicated by the low heart
rates. Hart (1945) recorded blood pressures from four species of fresh-water fish
that were stunned, placed ventral side up and out of the water. Bulbus pressures
recorded ranged from 21/5 mm. Hg in the bullhead to 65/62 mm. Hg in a gizzard
shad. He showed that bulbus pressures tended to increase at higher heart rates.
Blood pressures reported here are lower than those recorded by Randall et al. (1965)
and Holeton & Randall (1967) from the same species offish. The techniques are similar
in all cases and the differences in blood pressure are probably related either to a
seasonal effect (the present study was carried out in the winter whereas the other
studies were carried out in summer), to a temperature effect, or to intraspecific
differences between the various stocks of fish used. The study of Randall et al. (1965)
was carried out in sea water whereas the other two studies were carried out in fresh
water. A comparison of the results of Randall et al. (1965) with those of Holeton &
Randall (1967) would indicate that salinity has only a minor effect on blood pressure.
Temperature changes affect heart rate (Grodzinski, 1955; Labat, Raynaud & Serfaty,
1961), an increase in temperature producing an increase in heart rate via an aneural
mechanism (Laurent, 1962). Thus it would appear probable that the differences between
blood pressures recorded here and those reported by Holeton & Randall (1967) and
Randall et al. (1965) are best explained in terms of differences in the temperature of
the environment.
Satchell (1965) found that blood flow in the caudal vein increased when an isolated
trunk preparation of an elasmobranch was stimulated electrically. He also demonstrated the presence of valves, which prevented the backflow of blood from the caudal
veins into the segmental veins during activity. These valves do not appear to be present
in the trout, since latex paint will pass into the segmental veins when injected into the
caudal vein.
Activity in the trout results in intermittent increase in blood pressure in the subintestinal vein, but a decrease in blood flow through this vessel. There must, however,
be an increase in venous return to the heart during swimming as there is an increase
in cardiac output (Stevens & Randall, 1967). The increased pressure but decreased
flow through the subintestinal vein indicates that venoconstriction is occurring, perhaps in the liver through which the blood from the subintestinal vein passes before
entering the heart, and that the increased venous return to the heart during swimming
is being shunted through some other venous pathway.
The results of the experiments using atropine injections indicate that the increases
in heart rate occurring during swimming in the trout are aneural in origin. There are
no sympathetic fibres innervating the fish heart (Couteaux & Laurent, 1957), and all
efferent nerves appear to be cholinergic (Randall, 1966) and can be blocked with
atropine. A decrease in vagal tone during activity, however, may account for a part of
the cardio-acceleration in some species of fish under certain conditions.
In a single experiment carried out on the sucker (Catostomus tnacrocheilus) injections of atropine into the pericardial cavity of the resting fish produced a large increase in heart rate (Table 3). During swimming there were increases in heart rate of up
to 75 % of the resting level. The heart rate of the fish during activity was similar
before and after the injection of atropine into the pericardial cavity. Thus in the sucker
there is vagal tone to the heart under normal conditions, which is released during
Changes in the rainbow trout whilst swimming
313
activity. Therefore, the magnitude of the increase in heart rate during swimming in fish
is related to the extent of vagal tone. In the trout there is normally no vagal tone, and
only a small increase in heart rate during swimming; in the sucker there is extensive
vagal tone and a large increase in heart rate during activity. Thus there appears to be a
neural and an aneural mechanism operating in controlling heart rate. The increases in
heart rate during activity observed in the trout were aneural, whereas those in the
sucker had a neural as well as an aneural component.
Increases in vagal activity during hypoxia result in bradycardia (Randall, 1966).
Locomotory activity during hypoxia results in a large increase in heart rate in the
trout, so that a fish in hypoxic conditions has the same heart rate during activity as a
fish in an air-saturated environment. Thus it would seem that the larger increases in
heart rate (but from a lower initial level), observed in a trout in a hypoxic environment
are due in part to a release of vagal tone.
Table 3. Results of a single experiment on a sucker which show the effect of
exercise and atropine on respiratory rate and heart rate
Heart rate
Pre-exercise
During exercise
Post-exercise
Atropine into
pericardial cavity
During exercise
Post-exercise
38
74
35
55
Respiratory
rate
37
60
18
18
67
64
61
34
Johansen (1962) reported that activity in the cod was not associated with any changes
in heart rate. He also demonstrated that experimental increases in venous return caused
increases in stroke volume rather than changes in heart rate. Labat et al. (1961)
reported that increasing venous return in the catfish caused an increase in heart rate
that could be abolished with atropine. In the experiments reported here no correlation
could be found between the increased heart rate observed and the intermittent increases
in venous pressure recorded from the subintestinal vein.
Nakano & Thomlinson (personal communication) have measured increases in
blood catecholamines during activity in rainbow trout. Intravenous injections of
physiological doses of epinephrine (1-0-5-0 fig.) caused an increase in heart rate and
blood pressure. Shepherd (1965) observed a cardio-acceleration in dogs with denervated hearts which was independent of the level of circulating catecholamines.
Jensen (1963) have isolated a cardio-accelerator substance from the hagfish heart
which is not a catecholamine. Breton et al. (1964) have observed an increased heart rate
after electrical stimulation of an isolated teleost heart. Each of these observations
indicates the possibility of an endogenous supply of a cardio-accelerator substance
which is released by some aneural mechanism and which causes the observed increase
in heart rate in the trout during swimming. At present, however, the nature of the
mechanism producing the aneural cardio-acceleration of the trout heart during swimming is not understood.
Giaja & Markovic-Giaja (1957) reported that activity did not increase the rate of
respiration in teleosts, but Saunders (1962) demonstrated a large increase in ventilation
314
E. D O N STEVENS AND D. J. RANDALL
volume during swimming in a number of teleosts. The increases in respiration rate
recorded in this study could not be correlated with any changes in POa or P COa in the
venous or arterial blood (Stevens & Randall, 1967). Because the changes in breathing
rate occurred concomitantly with changes in muscular activity, the most logical explanation for the regulation of breathing rate during swimming in fish would appear to
be a mechanism similar to the Harrison joint-tendon reflex of mammals.
SUMMARY
1. Changes in blood pressure in the dorsal aorta, ventral aorta and subintestinal
vein, as well as changes in heart rate and breathing rate during moderate swimming
activity in the rainbow trout are reported.
2. Blood pressures both afferent and efferent to the gills increased during swimming
and then returned to normal levels within 30 min. after exercise.
3. Venous blood pressure was characterized by periodic increases during swimming.
The pressure changes were not in phase with the body movements.
4. Although total venous return to the heart increased during swimming, a decreased blood flow was recorded in the subintestinal vein.
5. Heart rate and breathing rate increased during swimming and then decreased
when swimming ceased.
6. Some possible mechanisms regulating heart and breathing rates are discussed.
This work was supported by grants from the National Research Council and the
B.C. Heart Foundation. We wish to thank the Pacific Biological Station, Nanaimo,
and particularly Dr J. R. Brett, for support and facilities made available for this
investigation.
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